Magnetic suspension



July 26, 1960 Filed June 20, 1955 R. w. GILBERT 2,946,930

MAGNETIC SUSPENSION 2 Sheets-Sheet 2 FEEDBA 0x ronas 25 \MO vsuz/vr or sus smoso mss may POINT OF EOU/L/BR/UM 27 0. c. AMPLIFIER 1v /f L $28 vMl 32 3/ 29 Li J ROSWELL m GILBERT INVENTOR.

MAGNETIC SUSPENSION Roswell W. Gilbert, Montclair, Nil, assignor, by mesne assignments, to Daystrom, Incorporated, Murray Hui, N J a corporation of New Jersey Filed June 20, 19-55, Ser. No. 516,517

" comma. (Cl.31 7--123) This invention relates toa method of and apparatus for the suspension of a magnetized or magnetizable object in free space by unidirectional and generally steady-state linkage of magnetic flux.

Magnetic fields have been used in many devices for suspension in the form of thrust bearings and the like, but contact restraint has been found necessary in at least one direction. Of course, alternating magnetic fields have been used for full suspensions, but they are not static in the'sense here intended.

The full magnetic support of an object in free space by static magnetic force, that is, by a purely steady-state linkage of magnetic flux, has been considered by many as posing a fallacy. Any attempt to suspend an object entirely by a stationary magnetic field results in at least one unstable direction.

I have found that feedback techniques may be applied to compensate for the metastable condition effectively to produce a stable suspension. Feedback is capable of providing impedance parameters of negative sign as a practical operation, to produce apparentinversions in systems connected thereto. In this case, the physical result is admittedly peculiar, but the qualitative theory here presented agrees with experiment and is peculiaronly in the concept of negative impedance which is a perfectly valid extension of electrical theory.

For example, a mass may be suspended in a fashion leaving one unstable direction, such as a simple attraction of a ferro-magnetic mass or article by an overhead permanent magnet or electromagnet. The system may then be coupled to an outside source and, by feedback techniques, the sign of the supporting force gradient may be reversed. The system thereby becomes stable in the previously unstable direction, but it is still truly static in the sense that energy is exchanged only in incremental amounts in response to disturbing forces.

An object of my invention is the provision of a method of suspending a magnet, or other ferro-rnagnetic mass or object, in free space, using only a primary, spaced magnetic support directly thereabove and surrounding solenoid means to which is connected an electrical feedback system to apply only incremental electromagnetic force thereto to act if, as and when the object departs from its equilibrium position, in order to effectively stabilize its suspension.

An object of my invention is the provision of apparatus for suspending a magnet, or other ferro-magnetic mass or object, in free space, said apparatus comprising an overhead primary magnetic supporting means, a coil surrounding the object, and a feedback system connected to said coil means and adapted to apply incremental electron-iagnetic force to the suspended object only as it departs from its equilibrium position.

These and other objects and advantages of the invenpurposes of description and are not to be construed as defining the scope or limits of the invention, reference being had for the latter purpose to the claims appended hereto.

In the drawings, wherein like reference characters denote like parts in the several views:

Figure 1 is a diagram representing a coil spring suspension of a magnetizable mass or magnet which is surrounded by a solenoid coil;

Figure 2 is a diagram illustrating the equivalent electrical network of the Figure 1 system;

Figure 3 is a graph showing the relationship between overstretching or understretching of the spring and the excess or deficiency in the spring lifting force thereby developed;

Figure 4 is a diagram which represents a suspension, generally like that of Figure 1 but modified by replacing the coil spring by a permanent or electromagnet alined to develop a supporting force on the suspended mass, said suspended mass being surrounded by a solenoid coil connected to a negative impedance device;

Figure 5 is a'diagr'am showing an electrical network equivalent to the arrangement of Figure 4;

Figure 6 is a graph showing the relationship between movement of the suspended mass and the deficiency or excess in the lifting force thereby available from the suspending magnet;

Figure 7 is a graph showing what is provided by the magnetic impedance feedback to the solenoid coil to stabilize the support by the suspending magnet; and

Figure 8 is a wiring diagram of a practical embodiment for feedback suspension, in accordance with my invention.

Referring now to the drawings, there is shown in Figure 1 a simple structure comprising a magnetizable mass or magnet 11 suspended by a coil spring 12 from a fixed support 13. The suspension is obviously stable because the force/deflection gradient of the spring is positive, as represented by the graph 14 in Figure 3. A coil 15 is coupled to the magnet so that current in the coil will exert a force upon the magnet and, conversely, motion of the magnet will induce a potential within the coil. Looking into the coil terminals, the system appears as the equivalent electrical network illustrated in Figure 2. In this figure, the mass of the magnet 11 appears as a capacitance C, the spring compliance as an inductance L, and frictional losses as a shunting resistance R, eifectively damping the system. The coil resistance R,, appears as itself.

The Figure 1 system may be considered as stable because the exponential time-constant of damping, L/R, is positive. When the system is displaced, as by pulling down or pushing up on the magnet 11, the produced disturbance decays to a point of stable equilibrium.

Figure 4 shows a generally similar system modified by replacing the coil spring 12. by a magnet 22 (indicated as a possible electromagnet by showing a surrounding coil 20) suspended from a fixed support 23, and in line to develop a supporting force on the suspended magnetizable mass or magnet 21. This arrangement is recognizably unstable, because the sign of the supporting compliance is now negative, and the force/deflection-or-movement gradient is the reverse of that in the Figure 1 system, as indicated by the graph 24 of Figure 6. The inductance, in the equivalent network represented in Figure 5, now appears negative in sign, and the time-constant of damping,

L/R, is likewise negative, In this Figure 5, the referencecharacters correspond with those of Figure 2. The system is unstable and the suspended object 21 will drift away from its metastable equilibrium point.

In order to stabilize thesystem, we connect to'the terminals, as indicated in Figure 5 a negative resistance 2 a source, -R .in an amount suflicient to at least compensate for R so that;

The "damping; resistance .R' will' new be shunted by -a 'or'positi-vein sign; Thesystemrwillmowbe stable:

The LOVEIfill" resistance-5; by itself is.:unstable, and thenegative inductance by itself iszunstabler: But'.the:;two

are .mutuallyista-ble. Negative resistance. applied :to-fihe Figure 1 system wouldima-ke it unstable-initheisamesense'i.

that-.positive sresistancexapplied'ttorz-theaFigure 4 system canuotnmakez-it-sstable zn fixpzessing thezmatten dilferently, it isspoint ed out that-rt positive resistance is always a receiver of energy, where-.=

as.negativeresistancez'is: always-a source of energy. I The equilibrium condition 0f .the Figure .1 system :islcthe state: ofiminimumccontained energy, and it delivers energy in-re:-- turningttora .statezcf-equilibriumz. The reverseis true int-the Figures-4 system, 1 the equilibrium fconditionsis the point of maximum:contained...energywand a.return to suclr; condition :Iequires :a receipt of energy; as from a negative resistance-1; a

This-.situationcisg'shown graphically inFigures 6 and 7, :Wherte'the'tgrapln 24'01? .Figure16 shows that as the-mass Zhinevessrlowm(represented as, to: the arighh in theafig-i ure), from the magnet 22, the suspendingforce decreaseszs That--is;;the.difierentialofithat, force over the tive, -.as;shewn bythe left'hand portion ofthergraph 24, 0r.- -.that;.to-.-:the-.left'of the :neutrallor zero position...

ThisF-Lahsence of stable: equilibriumv is? necessarily avoidedxibyasomething which gives a an effect generally equivalentrtothat represented by the. graph 25 in Figure;z:7, wherethe-suspending force increases as. the position,.rofi the suspended mass is lowered, and decreases as the position of the suspendedmassisiraiseda Thisnecessary stabilizingiorce is what is supplied by the feed-' back .sarrangement, tor-thereby at least. neutralize the unweightxof thetzsuspended;magnets 21 ibecomes negativer Uponiraismgythe' masse21 the differentials-becomes posi-u stable; influence .of the. lifting. magnet .22, represented by thet'graph :24;

FigureS shows a wiringdiagram representing a .practi:

calaembodiment'wherein the efifective negative resistance is {obtained by. feedback through a direct current amp1i-- tiers-26;: Themsolenoid around. the suspended mass-or magn. 7:,:is.here. divided into two coils, 28 and 29,1 in a mutual configuration to entirely avoid the self-resistances oft-the coils: This reduces-the coil resistance of the equivalent .network to Zero sozthat the appliednegative resistance is fully eifective. The pick-up coil 29 is connectedto;the'input side;0f the. amplifier-by leads 31 and 32, one ofsaidleadsincluding the coupling resistor R}. The; output-.side-of the amplifier. is connected to the exciting;coil,28 through leads 33 and 34, :oneof said leadsi includin-gnthe same coupling resistor Rf. The: feedback amplifier is thus connected fromtthe pick-upt coil 29 to theieexcitation: coil 28; with the .mutual inductance in .9

positive v or: degenerative, sense. Negative resistance isdevelopedby a resistor R mutualto both coilcircuits, in

regenerativesenseand, therefore,a regenerative resistor.

It will be, apparent that the feedback through the:cou-. pling resistor R eis positive and 'IhllS 'normallyunstabl'et It is.he,re stableonly' because of the coupled-negative.

inductancepresented bythe; suspension. litheeuspended mass. .27.,were; clamped the. systemwould fall. away from.

itsJmStabIe equilibrium point, but'when free the system willlrelapse. to. a stable.equilibriumpoint .in theiashion of "the intrinsically stable Figured system..,. This. nee-H essary negative resistance, '11,, is.thus developed by a resistor'mutual to both'coil circuits inia regenerative sense? Ifdesiredy'a high conductivity damping plate 35 may be disposed beneath the suspended magnet 27, and thereby included in the system as shown, to damp any motion which may be developed.

The concept of negative inductance is unusual but apparently valid although it perhaps has no counterpart in any actual electrical component except in a feedback system. Importantly, thenegative inductance contains 7 its maximum energy-rat =zero:current andtperhaps is better visualized in terms of. entropy, but it appears as a direct extension s;of: wellestablished theory -of 'electro= mechanical coupled systems/abysimplyreversin'g'-the sigi1 of the compliance. V

. 'In operation, the system will:seek-its-: eqi1ilibrium position, at which point the excitation current to the amplifier will reduc'eto zeros -If the'suspended magnet moves below its equilibrium position, the current developed in the surrounding coils 29 will exert a lifting force thereon to prevent its dro ping ,from a suppo PQ 'ition. lfjperchance, itshould .rise,.abov,e itsequilibrium positiony-a reversecurrentiwill.develop to,pullqitback to.

its equilibrium position. 7

Frorntheforegqing, it.will-,beseenethatl have pro;-

vided a method, and apparatus, for suspending magnetizr able material in free space: Asv an example. of.the ..use-.. fulness of such. an inventiomt-it is pointed out that inf-Gerriv tain nucleonic instruments, sush -as: ion ;charirbers,zinsula.--. tion leakage sets a limit to sensitivity despite-the.excel lencecf such f'insulati-ng. materials. as Tefion and. polyethylenec For: example, .achargedtbodymapb suspended a anionizable-eatmosphere and the loss oflcharge byi; ionic? conduction throughrthe igasznsed -.as. a measure .of ionization... At low; radiation levels, such. a structure; may have a loss time-constant of weeks,-or evenofyears v if the supporting insulation can -:be made perfect. The

to the body, in the fashionnof a vibrating :reed electrome ter, without physical contact therewith.

Having now described, my invention in. detail. in 7 accordance with the-requirements .of-the patent statutes;:. various. changes and; .modificationmwill suggest themselves --t0 those skilled, in this. art, and it is I intended that such changes and modificationsshaH -fall within the scope. and spirit I of the."invention, -as.,-recited .in.-the following. 1

claims I claimz.

1. Apparatus for suspendinga bodyof magnetizablematerial.--. in :free space solely by magnetic :forces, 5 comprising primary .static; magnetic supporting. means proxi mate tothe body, coilameanssurrounding. thebody; anda feedback. systemconnected. to said coil means-to apply incremental, stabil ling electromagnetic .forces. to. thebody; inresponse-tochanges-in -tl1'e fi-ux linkage between the bodyv and the static; magnetiesupporting means.

2. Apparatus for-suspending ;in tree space entirely magnetic forces a mass including magnetizahleflmaterial;..

comprising prima-ry-static:magneticsupportingv means dis:

posed above said material;ssolenoidcoil means-surroundai ingsaid material, and a feedback system connectedto-saidir coil means; to apply incremental; stabilizing ;electrornag. netic; forces to said.suspendedmateriahato' assist=the:-pri-- mam: magneticiorcesswhen the-suspended materialitends to fall, and. ,to oppose said.primary forces; when..said--.

material tends to rise. I

3. The. invention as recited 'in,,clai mv 2, wherein. the

feedback systemcomprisesan amplifier, a .resistoncor'm, nected to; an1 inter'm ediate pointof". the solenoid coill'. means, dividiri'g saidfmeans into an .exciting'poil and {a pick-up coil, in which said pick 'up coil isconnected to the input side of the amplifier and the exciting coil is References Cited in the file of this patent connected to the output side of said amplifier, with the resistor common to both circuits, whereby the entire UNITED STATES PATENTS feedback system, acts as a negative resistance. 1,707,822 Stock Apr. 2, 1929 4. The method of stalilizing the metastable equilibrium 5 2,081,367 Nicolson May 25, 1937 of a body of magnetizable material suspended in free 2,256,937 Beams Sept. 23, 1941 space solely by static magetic forces, which method corn- 2,602,660 Shannon July 8, 1952 prises applying secondary incremental magnetic equaliz- 2,647,323 Johnson et a1. Aug. 4, 1953 ing forces to the body in response to changes in the flux 2,675,222 Clark Apr. 13, 1954 linkage between the body and the static magnetic forces. 10 2,852,243 Shepard Sept. 16, 1958 

